Functional and structural neuroimaging studies of delayed reward discounting in addiction: A systematic review.

Given the robust behavioral association between delayed reward discounting (DRD) and addictive behavior, there is an expanding literature investigating the neural correlates of this relationship. The objective of this systematic review was to characterize and critically appraise the existing literature examining the neural correlates of DRD in individuals exhibiting addictive behavior using functional and structural MRI (fMRI/MRI) and to do so through the lens of the neural networks implicated in addiction. Using a systematic search strategy, 20 studies were identified, with 12 focusing on task fMRI, 4 focusing on functional connectivity fMRI, and 4 focusing on structural MRI. Behaviorally, significantly steeper DRD was present in individuals with addictive disorders across studies, reproducing earlier findings. Among individuals with addictive disorders, there was substantial evidence of greater neural activity in the executive control network during choices for larger-delayed rewards (delayed gratification) relative to choices for smaller-immediate rewards (immediate gratification), particularly in dorsolateral prefrontal cortex, as well as moderate evidence of greater recruitment of the default mode, salience, and reward valuation networks during larger-delayed choices. In functional connectivity fMRI studies, there was moderate evidence for greater connectivity between the executive control, salience, and default mode networks in individuals exhibiting addictive behavior. Structural MRI studies reported highly heterogeneous findings and no consistent conclusions could be drawn. As a whole, this review suggests consistent differences in neural activation and connectivity relating to DRD in individuals with addictive disorders. It also reveals heterogeneity of methods and findings in this line of inquiry. (PsycINFO Database Record (c) 2019 APA, all rights reserved).